Sensitometric modification by pre-exposure

ABSTRACT

The sensitometric properties of multicolor diffusion transfer film units may be modified after the photosensitive element has been coated. Sensitometric modification is effected by a uniform exposure of the photosensitive element to light of a predetermined intensity and wavelength range. In accordance with this invention, the slopes of one or more of the individual D log E curves may be modified to bring said curves into a more parallel relationship with each other.

PATENTEUauuzsmm SHEET 2. BF '4 REFLECTION DENSITY FIG2 PATENTED Z BN sum 3 or 4 LOG EXPOSURE w o. .CWZUO ZOTPOU EUE FIG 3 REFLECTION DENSITY SHEET k 0F 4 LOG EXPOSURE FIG.4

SENSITOMETRIC MODIFICATION BY PRE-EXIPOSURE This invention is concerned with photography and, more particularly, with the formation of multicolor photographic images.

It is well known that photographic films, and especially multicolor films, may and generally do vary from lot to lot, notwithstanding efforts to repeat7 previous films.

Manufacturers of multicolor photographic films have developed a number of procedures to minimize the efstored for a period of time after coating to allow the films to age, so that changes in sensitometry following coating have an opportunity to reach a plateau prior to sale. If the film is designed to be developed by a photofinisher or in a darkroom, processing of the exposed multicolor film is controlled within very narrow limits, typically within plus or minus a half degree of a prescribed temperature, in order to minimize sensitometric variations from film to film. Where the multicolor film is of the negative type, an opportunity to adjust the sensitometry occurs in printing the desired final positive image, during which operation the printing exposure may be appropriately color filtered.

Obviously the basic sources of sensitometric variations noted above exist also in multicolor diffusion transfer films, with the added complication that once the film is shipped, the sensitometric properties are essentially fixed. The opportunity for adjustment provided in darkroom processing, practically speaking, is unavailable for users of self-developing films. While professional and advanced amatuer photographers may be skillful enough to utilize color correction filters to least partially rebalance the color balance, ordinary users of the film would only be confused by such additional operations; more important, however, is the fact that the use of color correction filters usually results in a reduction of the effectivefilm speed.

In the manufacture of multicolor diffusion transfer film, it is possible ,to make small changes in the color balance of the resulting multicolor transfer image by making small changes in the concentrations or ratios of some of the components of the processing composition. This technique, while quite useful, is limited to correction of minor imbalances in the color balance of the final image. In addition, this correction technique may require preparation of a'specific processing composition for each lot of the multicolor photosensitive element, resulting in an uneconomical inventory of a plurality of different processing compositions, including some which are potentially obsolete.

The present invention is directed to this problem. A primary object of this invention is to provide a simple and economical method of modifying the sensitometry of a multicolor film subsequent to the manufacture thereof.

A further object of this invention is to provide multicolor films, particularly multicolor diffusion transfer films, wherein at least one of the blue-, greenand redsensitive silver halide emulsions contains a weak nonimagewise latent image.

Yet another object of this invention is to provide processes for manufacturing multicolor photographic films, wherein at least one of the blue-, greenand redsensitive silver halide emulsions is given a uniform,

non-imagewise exposure to light of a predetermined wavelength range and intensity.

Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.

The invention accordingly comprises the method involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of components which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a somewhat schematic, perspective view illustrating a method of fabricating and assembling a succession of one type of photographic diffusion transfer multicolor film units, the sensitometry of which may be modified in accordance with this invention at some stage of the fabrication and assembly subsequent to coating the multicolor photosensitive element;

FIG. 2 is a graphic illustration of the blue, green and red D log E curves of a multicolor reflection print obtained by diffusion transfer processing a multicolor photosensitive element and which may be considered to, be a control for purposes of illustrating this invention; and

FIGS. 3 and 4 are graphic illustrations of the blue, green and red D log E curves of two multicolor reflection prints obtained using the same components as used in obtaining the D log E curves shown in FIG. 2 except that the photosensitive elements were given a weak preexposure in accordance with this invention, the curves of FIGS. 3 and 4 thus illustrating the modification in sensitometry provided by this invention.

As noted above, the present invention has special applicability to multicolor diffusion transfer films; for convenience, the invention will be illustrated by reference to multicolor diffusion transfer films designed to provide integral negative-positive reflection prints. In such prints, the photograph comprises the developed silver halide emulsions retained with the dye-image-- carrying layer as part of a permanent laminate. The image-carrying layer is separated from the developed silver halide emulsions in said laminate by a lightreflecting layer, preferably a layer containing titanium dioxide, Illustrative of patents describing such products and processes are US. Pat. No. 2,983,606 issued Mar. 9, 1961 to Howard G. Rogers, US. Pat. Nos. 3,415,644, 3,415,645 and 3,415,646 issued Dec. 10, 1968 to Edwin H. Land, US. Pat. Nos. 3,594,164 and 3,594,165 issued July 20, 1971 to Howard G. Rogers, and US. Pat. No. 3,647,347 issued Mar. 7, 1972 to Edwin H. Land.

Referring more specifically to the aforementioned US. Pat. No. 3,415,644, said patent discloses photographic products and processes employing dye developers wherein a photosensitive element and an imagereceiving layer are maintained in fixed relationship prior to photoexposure and this fixed relationship is maintained after processing and image formation to provide a laminate including the processed silver halide emulsions and the image-receiving layer. Photoexposure is made through a transparent (support) element and application of a processing composition provides a layer of light-reflecting material to provide a white background for viewing the image and to mask the developed silver halide emulsions. The desired color transfer image is viewed through said transparent support against said white background.

The color characteristics and qualities of multicolor images are conventionally expressed in terms of the H and D" or D log E curves of the blue, green and red exposure records contained in the multicolor image. D log E" curves present the relationship of image density to the exposure resulting in the recorded image density, and the D log E curve is obtained by plotting the measured optical density against the logarithm of the exposure providing the measured density. Such curves may be readily plotted for diffusion transfer multicolor positive images, the maximum transfer density being a measure of the minimum exposure received by the silver halide and the lowest transfer density being a measure of the maximum exposure received by the silver halide. Customarily, the portion of minimum densities (D,,.,-,,) of the D log E curve is referred to as the toe portion, and the portion of the curve reproducing maximum densities (D,,,,,,,) is referred to as the shoulder portion. The portion of the D log E curve over which the gradient or slope of the curve is substantially constant, customarily referred to as the straightline portion, is a measure of the exposure range over which the density is proportional to log E and this portion of the curve may be considered an indication of the latitude of the film.

In analyzing multicolor images for color quality, reading" the blue, green and red D log E curves provides a means of expressing the relationship of these curves to each other, a relationship frequently referred to as color balance. If, for example, the skin tones appear greenish or bluish on visual inspection the extent of the apparent color imbalance may be quantitatively depicted by plotting the blue, green and red D log E curves on the same graph. If the slopes of the blue, green and red D log E curves match, i.e., they are the same or substantially the same, then the color film may be considered to be in sensitometric balance. It is not necessary that the several curves overlie one another. In practice, integral blue, green and red reflection densities are used; these densities are called integral because they measure the total density at a given wavelength independent of the dye or dyes responsible for that density.

While the D log E curves are considered to be a measure of the effect of variations in exposure upon the final image density, in reality they measure the amount of each dye controlled by the photographic system. Photoexposure is, of course, the major source of this control. Variations in manufacturing steps and storage prior to use also may have significant effects upon the amount of silver halide developable during processing,

thus affecting the final response characteristics of the silver halide emulsions in ways adversely affecting color balance.

It has been found that imbalances in the color sensitometry of a given photographic system may be at least substantially, if not completely, reduced (corrected) by giving the photosensitive element a non-imagewise exposure to light of selected wavelength range(s) and intensity subsequent to coating of said photosensitive element. This non-imagewise preexposure imparts a weak latent image of predetermined characteristics and thereby permits controlled modifications of the sensitometry of an already coated and aged photosensitive element. Desirable changes in color balance thus may be readily effected by changes in one, two or all three of the individual red, green and blue H and D curves. Reliance upon modifications of the processing composition to offset imbalances in the color sensitometry of the photosensitive element itself are greatly reduced, in many cases even to the point where a common processing composition may be used with all or almost all runs of the photosensitive element.

Although the preexposure contemplated by this invention adds the same absolute amount of exposure to each part of the D log E curve, the effect is to add a proportionately larger exposure to the shoulder portion of the positive curve. As a result, the slope of the shoulder portion is changed and one may say that the shoulder portion is bent over." This makes it possible to change the slope of an individual blue, green or red D log E curve. In addition, an individual curve also may be caused to slide over to more closely overlie one or both of the other curves, in whole or in part, if such a relationship is found desirable; this type of change in sensitometry may be used to change the film speed of one or more silver halide emulsions.

In practice, the preexposure may be to a specific wavelength range, e.g., to blue, green or red light, or it may be to a combination of several colors, or to both white light and a specific wavelength range or ranges. Indeed, it may be desirable in a given instance to preex pose to two different wavelength ranges in a ratio such that one silver halide emulsion receives more preexposure than does another. Such differential preexposures may provide useful interimage effects.

A wide variety of color filters are commercially available and may be used in the practice of this invention, including the well known Wratten filters. The light transmission characteristics of many suitable filters are described in Kodak Filters For Scientific and Technical Uses, published by Eastman Kodak Co. as Kodak Publication No. 8-3. If necessary, filters of special light transmission characteristics may be readily prepared.

The preexposure contemplated by this invention is most advantageously applied after the photosensitive element has aged to maturity, i.e., the sensitometry of the photosensitive element as manufactured is no longer changing significantly with time. Indeed, the beneficial effects of preexposure may be offset, in whole or in part, by ageing changes if the preexposure is effected before the photosensitive element has completed ageing. In the same sense, the image-receiving system and the processing composition also should have reached their maturity prior to determining the desired preexposure.

I The implementation of this invention may be more readily understood if further description is made in the context of a specific diffusion transfer film.

Multicolor diffusion transfer images may be obtained usinga variety of arrangements of the image-receiving layer and the silver halide emulsions. Thus, these layers may be carried by a common support or by separate supports brought into superposition after photoexposure. A particularly advantageous film" structure is shown in the aforementioned U.S. Pat. No. 3,415,644 wherein the requisite layers are in superposed relationship prior to and during photoexposure, and these layers are maintained in superposed relationship as a permanent laminate after processing and image formation. Such film'units typically contain an outer transparent layer or support through which photoexposure is effected and the final multicolor image viewed, and another outer layer or support carrying at least the photosensitive layers, the latter support preferably being opaque. While these supports or sheet-like elements may simply be. held in superposed relationship, e.g., by a binding tape'around the edges, in the preferred embodiment these elements are laminated together prior to photoexposure. This prelamination provides a number of benefits, both during manufacture and in photoexposure. Following exposure, the elements are delaminated by the distribution of a fluid processing composition which, upon solidification, bonds the elements together to form the desired permanent laminate. Procedures for forming such prelaminated film units wherein the two elements are temporarilylaminated together prior to exposure are described, for example, in U.S. Pat. No. 3,625,281 to Albert J. Bachelder and Frederick J. Binder and in U.S. Pat. No. 3,652,282 to Edwin H. Land,'both issued Mar. 28, 1972. A prelaminated integral film unit is easier to handle and manipulate during assembly and during exposure'and processing within the camera; it is more compact and hence, permits smaller and less bulky film packs and. cameras; and it is less subject to buckling and distortion due to temperature and humidity changes and more likely to lie flat and remain planar during exposure. Since the elements are in contact throughout the entire extent of their facing surface, every portion of each element is exposed to substantially the same ambient conditions so that each portion has the same physical and chemical properties as every other portion and the elements produce uniform results, the photographically active 1973). Film unit 10 comprises a first or photosensitive sheet 12, a second or image-receiving sheet 14, rupturable container 16 holding a quantity of a liquid processing composition, a mask or binding sheet 18, a trapping element 20 and a sealing strip 22. Sheets 12 and 14 are preferably rectangular, are substantially equal in width and arranged in superposed face-to-face contact with one another with the lateral edges of the sheets substantially in alignment. The second sheet 14 is substantially longer than the photosensitive sheet 12 and includes a leading end section 24 extending beyond the leading edge of sheet 12 by a distance slightly in excess of the shorter dimension of container 16 and a trailing endsection 26 extending a relatively short distance beyond the trailing edge of photosensitive sheet 12. In a preferred embodiment of the film unit, the photosensitive and image-receiving sheets are laminated to one another throughout substantially the entire area of their facing surfaces except for a narrow region adjacent the leading edge of the photosensitive sheet.

Sheets 12 and 14 are secured in face-to-face relation at their lateral and trailing end margins by binding sheet 18 which is generally rectangular in shape and formed with a rectangular exposure opening 28 slightly smaller than photosensitive sheet 12. Binding sheet 18 is preferably formed of a strong, light-opaque, white material such as, for example, a laminate including a layer of paper, a polymer and an opaque layer such as a metallic coating and/or pigment carried on or within a layer of sheet 18. The mask or binding sheet is larger than the image-receiving sheet 14 and includes a leading end section 30, a trailing end section 32 and lateral marginal sections 34 adapted to be folded over the edges of the film unit. Sheet 18 is adhered to the outer surface of sheet 14 substantially over the entire facing surfaces of the two sheets surrounding exposure opening 28. Lateral marginal sections 34 of sheet 18' are folded around the lateral edges of sheets 12 and 14 and secured to the margins of sheet 12. Trailing end section 32 of sheet 18 is folded around the trailing edge of sheet 14 and secured to the outer surface of photosensitive sheet 12 near the trailing edge thereof.

Container 16 is of the type shown in U.S. Pat. No. 2,543,181 and is formed by folding a rectangular blank of a fluid impervious sheet material medially and sealing the marginal sections of the blank to one another 1 to form a cavity for containing processing liquid. Coneffect their function. Moreover, processing, specifically, spreading of the processing liquid within the film unit, is facilitated since there is little or substantially no air between the sheets to interfere with liquid distributainer 16 is mounted on the leading edge section 24 of sheet 14 adjacent the leading edge of photosensitive sheet 12 in position to discharge its fluid contents between the photosensitive and image-receiving sheets. Container 16 is retained in place by portion of lateral edge sections 34 secured to the ends of the container and leading end section 30 of binding sheet 18 which is folded aroung the leading edge of sheet 14 and secured to a longitudinal edge of the container. Sealing strip 22 is secured to a longitudinal marginal section 36 of the container and the leading end margin of photosensitive sheet 12 and cooperates with the sheets to bridge the gap between the container and the photosensitive sheet and form a conduit for conducting the liquid from the container between the photosensitive and image-receiving sheets.-

In the processing of the film unit shown, the film unit is advanced, container foremost, relative to and between a pair of pressure-applying members which initially apply compressive pressure to the container to eject its liquid contents between the photosensitive and image-receiving sheets and then distribute the mass of liquid between the sheets toward the trailing ends thereof to form a layer of substantially uniform, predetermined thickness at least coextensive with the area defined by exposure opening 28. In order to insure sufficient processing liquid to form a layer of the required area and thickness between the sheets, excess processing liquid may be provided in container 16 and the film unit includes trapping means for collecting and retaining excess processing liquid overrun. In the form shown, these means comprise trapping element 24 shown as a narrow strip of a relatively thick sheet material formed with perforations and indentations 38 which occupy the major portion of trapping element 20. The trapping element is secured between trailing end section 32 and the trailing end margins of sheets 12 and 14 with the perforations and indentations 38 cooperating with sheets 12, 14 and 18 to provide spaces for collecting and retaining excess processing liquid overrun.

In the assembly method shown in FIG. 1, component transport is achieved by utilizing a common component of the film units themselves as the means for transporting the components throughout the major portion of the fabrication and assembly operations. This common component is the mask or binding sheet 18 which is initially provided in the form of an elongated web or strip designated 40 in FIG. 1, the locations at which strip 40 is folded and cut to provide mask 18 being indicated by dot-dash lines. Strip 40 has a width substantially equal to the length of binding sheet 18 and remains intact as a continuous strip throughout all but the last two assembly operations. Thus the components of the individual film units are mounted on and attached to strip 40 as the latter is moved intermittently or continuously through the various fabrication, assembly and inspection stations at which the components of the succession of film units are assembled to form film units each having its longitudinal dimension extending in a direction transverse to the length of strip 40.

Strip 40 which forms a succession of binding sheets 18 is of substantial length, i.e., hundreds of feet, and has a width equal to the overall length of each binding sheet. It may be in coiled form and provision may be made for splicing the trailing end of a strip to the leading end of the next succeeding coil of strip 40 without interrupting the fabrication and assembly operation. The first operation performed on strip 40 as part of the fabrication and assembly process illustrated in FIG. 1, is a cutting operation in which the rectangular exposure opening 28 is formed and notches 42 and 44 are formed in the opposite lateral margins of strip 40 to prevent overlap and excessive thickness in the regions in which the mask sheet is folded around the edges of the image-recording sheet during subsequent assembly operation. The cutting operation may be performed by conventional means such as a punch and die.

Although the photosensitive and second sheets 12 and 14 may be brought into the assembly operation as separate, elongated strips, in the preferred embodiment illustrated, the photosensitive and second sheets (strips) are also supplied in the form of coils having widths equal to the lengths of the respective sheets and are laminated to one another prior to being brought into association with strip 40. The laminating process essentially comprises guiding the photosensitive and image-receiving sheet along converging paths into superposed relation, distributing a laminating liquid between the sheets and pressing them into face-to-face contact. For this purpose, a pair of laminating rollers 46 and 48 may be employed for advancing the sheets thereb'etween into face-to-face contact and pressing the sheets together with a nozzle 50 for introducing the laminating liquid between the sheet at the nip of rollers 46 and 48. A particularly useful laminating liquid comprises an aqueous solution of a water-soluble polyethylene glycol, as described and claimed in the copending application of Edwin H. Land, Ser. No. 247,023 filed Apr. 24, 1972.

The assembly process begins with the bringing together of a laminate comprising the photosensitive and image-receiving sheets, and carrier strip 40 and adhering the laminate to the carrier strip which thereafter functions to transport sections of the sheets (laminate) as well as the other components of the film units through subsequent fabrication, assembly and inspection operations. As shown in FIG. 1, the carrier strip 40 is moved upwardly over a guide 52 and then along a generally horizontal path through a succession of machine stations in which the assembly and inspection operations are performed. The laminate comprising photosensitive and second sheets 12 and 14 is advanced by suitable means such as a pair of rollers 54 and 56 into superposition with strip 40 at guide 52. The laminate is advanced from between rollers 54 and 56 between a knife 58 and anvil 60 operative to cut the laminate transversely to form a leading end edge normal to the lateral edges of the laminate. Both carrier strip 40 and the laminate are advanced into superposition such that the leading edge designated 62 of the laminate is located approximately one quarter of the distance from an edge of an exposure opening 28 in strip 40 and the adjacent edge of the preceding exposure opening.

In the assembly process, strip 40 may be moved either continuously or intermittently, the latter method being illustrated in FIG. 1, and motion of strip 40 and the section of the laminate are arrested with the leading edge margin of the laminate, located with respect to strip 40 as previously indicated, disposed between the jaws, one of which is shown and designated 64, of a heat sealing device adapted to apply heat and compressive pressure to strip 40 and the laminate to bond the leading edge portion of image-receiving sheet 14 to strip 40. For this purpose, the upper surface of strip 40 is coated with a conventional heat activated adhesive formed, for example, of a thermoplastic polymer. Carrier strip 40 is then advanced to a second heat sealing station including a pair of juxtaposed jaws one of which is shown and designated as 66, for sealing the imagereceiving sheet to carrier strip 40 in the region completely surrounding the exposure opening 28 in the carrier strip. Subsequent to adhering the leading edge portion of the laminate to strip 40 at the heat sealing station including jaw 64 and prior to or during movement of the strip and laminate into the second heat sealing station including jaw 66, knife 58 is actuated to sever the laminate to the desired length and the strip is caused to advance a greater distance than the laminate to provide spacing between the trailing edge of the section of the laminate severed from the remainder of the laminate and the new leading edge of the laminate formed by actuation of knife 58. This motion is sufficient to locate the leading edge 62 of the laminate with respect to strip 40 as previously described and between the heat'sealing jaws of the first heat sealing station. Thus the process is basically one of heat sealing the laminate to the carrier strip, advancing the carrier strip so as to move the laminate heat sealed thereto toward the leading edge, severing the laminate to length and then advancing the'next succeeding leading end portion of the laminate into position with respect to strip 40 to be heat sealed.

The primary reason for preferring prelamination of the photosensitive and second sheets, at least insofar as the manufacturing and assembly processes are concerned, will be apparent at this point. In the initial heat sealing operation, it is a section of the image-receiving sheet which is attached to the carrier strip so if the photosensitive sheet were not laminated to the imagereceiving sheet, provision would be required for at least temporarily attaching the photosensitive sheet to the image-receiving sheet which is in turn attached to carrier strip 40. In a manufacturing process in which the photosensitive and image-receiving sheets are not prelaminated by distribution of a laminating liquid, they may at least be temporarily attached to one another by heat sealing jaws located adjacent knife 58, preferably ahead of the knife and adapted to soften and bond to one another portions of the facing polymeric layers of the two sheets in regions which are located near the margins of the sheets in the completed film unit.

At the next station or stations in the film assembly apparatus, a container 16 is attached to an end lateral marginal portion of strip 40 which comprises leading end section 30 of mask sheet 18 and a trapping element 20 is mounted on a marginal section of strip 40 which comprises a trailing end section 32 of mask sheet 18. The container 16 is attached by heat sealing the longitudinal margin of the container located opposite marginal sections 16, by gripping the leading end section and the margin of the container between a pair of heat sealing jaws. Trailing element 20 is similarly mounted at the opposite edge of strip by compressing the element and trailing end section between a pair of heat sealing jaws. The trapping element may take the form of an elongated strip or web severed from the remainder thereof immediately prior to or subsequent to adherence by heat sealing to carrier strip 40.

Each container 16 may be formed as one of a succession of containers produced by a continuous process and severed from a strip of containers by a knife and anvil 68 and'70 immediately prior to or subsequent to heat sealing of the container to carrier strip 40. In the embodiment shown in FIG. 1, sealing strip 22 is heat sealed to a longitudinal marginal section 36 of container 16 prior to severance of the container from the remainder of a strip of containers. Sealing strip 22 may also take the form of an elongated, coiled strip and heat sealing thereof to the strip of containers may be either a continuous or an intermittent operation performed by compressing the containers and strip 22 between a pair of heat sealing members one of which is shown as jaw 72 in FIG. 1. In this manner both sealing strip 22 and a container 16 are severed simultaneously and to the same length. As is previously noted, this may be accomplished either subsequent to or prior to adherence of the container to a margin of strip 40.

The next operations in the fabrication and assembly process are folding operations in which the leading end section 30 to which a container is attached and the trailing end section 32 to which a trapping element 20 is attached, are folded through so that the container is brought into face-to-face relation with the leading end section 24 of the image-receiving sheet and the trapping element 20 is brought into face-to-face relation with the trailing end sections of the photosensitive and image-receiving sheets and is confined between the trailing end sections and trailing end section 32 of sheet 18. The folding operations may be accomplished by conventional means such as plows and/or movable fingers such as are well-known in the art.

The next assembly operations involve the heat sealing of stip 22 to the leading margin of photosensitive sheet 12 and the heat sealing of trailing end section 18 to the photosensitive sheet near the trailing edge thereof. These heating sealing operations are accomplished by conventional means in the same manner as the previously described heat sealing operations, namely by compressing the sheets to be sealed to one another between a pair of heated jaws. Heat sealing of strip 22 and trailing end section 32 to the outer surface of the photosensitive sheet complete the assembly operations in which a succession of film units, in various stages of assembly and fabrication are coupled to one another and transported by carrier strip 40.

The fabrication and assembly apparatus will'also include a number of inspection stations which serve to insure that each successive fabrication and assembly operation has been performed correctly. These inspection means will include means adapted to determine, for example, whether or not the laminated and photosensitive and image-receiving sheets are properly aligned with strip 40; that the leading edge of each section of the laminate is properly located with respect to an exposure aperture; that trapping element 20 is attached to the carrier strip and is properly located thereon; that a container and heat sealing strip 22 are attached to the carrier strip and properly located thereon; and that the various folding and sealing devices have performed as required. Such inspection means are well-known in the art and include mechanical, optical and pneumatic devices for sensing the presence and/or location of the various components. The purpose of providing continuous monitoring of the fabrication and assembly process is to-promptly identify improperly fabricated or assembled film units immediately following the particular fabrication or assembly step being monitored so that action can be taken to correct the operation which is resulting in the defect and to promptly identify the defective film unit so that subsequent assembly operations are not performed thereon and components wasted, and the film unit will be rejected or set aside for salvage of components and- /or further remedial work at a subsequent stage in the manufacturing process.

Following heat sealing of the leading and trailing end sections 30 and 32 to the photosensitive sheet, the sucstations. In the first, lateral marginal sections 34 are folded and in the second station, sections 34 are heat sealed to the lateral margins of photosensitive sheet 12. During these last two steps, the film units are preferably advanced in a direction transverse to their previous direction so that folding may be accomplished by conventional means such as plows and/or fingers and the heat sealing steps may be performed either continuously as by advancing the margins of each film unit between pairs of heat sealing rollers, or intermittently by clamping the margins between heat sealing jaws two of which are shown in FIG. 1 and designated 78.

Upon completion of this last operation, the assembly of each film unit is complete and following a final inspection the film unit is ready to be loaded separately or together with other film units into a suitable lighttight container or cassette in which it is exposed within a camera.

As stated earlier, the present invention provides for modification of the sensitometry of a multicolor film by effecting a controlled, non-imagewise (uniform) exposure of the coated photosensitive element. This preexposure may be effected at any convenient stage of the fabrication and assembly operation. In the embodiment shown in FIG. 1, a preexposure station is provided just before the laminate 12 is cut into film unit-size segments and joined to the carrier strip 40. The preexposure station comprises a light source 84 positioned to expose a predetermined portion of the photosensitive sheet 12 through image-receiving sheet 14, a color filter 86. Where it is found to be desirable, a plurality of preexposure stations may be provided, each adapted to provide a non-imagewise exposure of a predetermined nature. Alternatively, a single preexposure station may include several different color filters, each having the requisite light transmission properties required to effect exposure to the desired wavelength range or ranges. If it becomes necessary to reduce the intensity of the light transmitted by the color filter, a suitable neutral density filter may be included in the light path. Suitable shielding means, not shown, are provided to prevent light transmitted by the filter(s) from striking unintended portions of the photosensitive element. The light source may be one which is pulsed, such as a strobe, in synchronization with the intermittent assembly operation shown in FIG. 1; appropriate indexing means may be provided to insure registration of the preexposed area with the image area defined by the mask 18. Because the preexposure step utilizes extremely low light intensities, the light source 84 will require replacement only infrequently, and its light emission characteristics will remain substantially constant for long periods of use.

In the embodiment shown in FIG. 1, the preexposure station is positioned just before the laminate 14 is severed into film unit segments mounted on the carrier web 40. Alternatively, the preexposure station may be positioned just before the knife 74 severs the carrier web 40 or at any other convenient stage of the fabrication and assembly operation, including effecting the desired preexposure before the photosensitive sheet 12 is laminated to the image receiving sheet 14. In the later instance, a continuous light source may be more efficient than an intermittent light source. While the preexposure step also may be preformed on the completely assembled individual film units 10, this altemative is less preferred because of the reduced ease of handling the individual film units as compared with the embodiments wherein preexposure is effected while the photosensitive element is carried by a carrier sheet, as in FIG. 1.

In the practice of this invention, a photosensitive element is exposed to a suitable multicolor step-wedge and diffusion transfer processed with a given processing composition and image-receiving element. The blue, green and red D log E curves of the resulting multicolor transfer image (control image) are prepared. Examination of these D log E curves will indicate to one skilled in color photographic sensitiometry the manner and extent to which the individual D log E curves depart from the desired curve shape. From this examination, one may determine by routine analysis and experimentation how much additional exposure would be required of what wavelength range or ranges to bring the individual D log E curve(s) closer to their desired shape(s). The photosensitive element of another film unit, having the identical photosensitive element, image-receiving element and processing composition as used in obtaining the control image, is then given a uniform exposure to light of the wavelength range(s) and intensity estimated to be necessary to provide the desired changes in the D log E curves of the control image. The blue, green and red D log E curves of the resulting test multicolor tranfer image are then prepared and compared with the control. While more than one test may be required to determine the preexposure effective to give the desired D log E curve shape changes, such tests may be performed rapidly and easily, and the number of tests required to determine the most suitable preexposure very rapidly decreases with experience.

The invention may be better understood by reference to FIGS. 2, 3 and 4. Blue, green and red D log E curves are reproduced in FIG. 2 for a control integral negative positive reflection print. FIGS. 3 and 4 illustrate the changes effected in the D log E curves as a result ofgiving another section of the same photosensitive element different preexposures followed by processing unsing the same image-receiving system and processing composition as used in forming the control integral negative-positive reflection print. Thus, all components of the film unit were kept constant and the differences in curve shapes result directly from the specific preexposures. In each instance, preexposure was effected using an E, G and G Mark 6 Sensitometer set at 10' seconds exposure using a Xenon strobe exposure source, with the photosensitive element approximately 6 inches from the light source. The D log and E curves reproduced in FIG. 3 were obtained following preexposure in the described manner through a 2.60 neutral density filter and a Wratten 21 color filter, while the curves reproduced in FIG. 4 were obtained as a result of preexposure through a 2.60 neutral density filter and a Wratten 23 filter. (The neutral density filters were used solely to reduce the amount of light passed by the Wratten filter without modifying the wavelength range(s) or wavelength ratios of that light.) A Wratten 21 transmits visible light above about 540 nm and appears orange in color; it passes less green than red light and no blue light. A Wratten 23 filter transmits visible light above about 560 nm and appears light red in color; it transmits a wavelength range similar to that of the Wratten 21 filter but effects less green exposure relative to the red exposure obtained with the Wratten 2l filter. A comparison of the D log E curves clearly shows highly desirable curve shape changes, providing increased" dynamic range and changesin slope bringing the individual curves into a more parallel relationship to give improved color balance and increased red speed. 1

It should be readily recognized that the particular components used in the above illustration are essentially immaterial since they were maintained constant except for the preexposure. While details of these components therefore need not be set forth, it may be noted that the photosensitive element, image receiving element and processing composition were essentially the same as those described in the above-mentioned copending application of Edwin H. Land, Ser. No. 247,023 filed Apr. 24, 1972, the same yellow, magenta and cyan dye developers being used and the photosensitive and image-receiving elements being prelaminated as therein described.

The preexposures described above were effected through the image-receiving element 14 subsequent to the lamination thereof to the photosensitive element 12. indeed, it has been found that the beneficial effects of preexposure for sensitometric modification are retained over a longerperiod if the photosensitive layers are part of a laminate between polymeric supports. While the reasons for this stabilizing effect of the laminate upon the preexposure beneficial effects are not known, it is believed that the insulation to changes in ambient conditions provided by the laminate is particularly significant. In addition, the polymeric supports provide protection against atmospheric components which might cause or facilitate fading of the latent image imparted by preexposure. The polymeric supports may comprise any of the conventional film base materials, and preferably are substantially impermeable to oxygen transmission. Polyesters, such as polyethylene terephthalate, are particularly useful'supports.

In general, the preexposure intensity is such as to provide a weak latent image, although the preexposure may be so low as to merely bring the resulting latent image to just below the threshold of developability. In practice it has been found that the preexposure level is such that any reduction in D contributed by the silver halide emulsion(s) preexposed as compared with the corresponding control is preferably no more than about 0.l to 0.2; higher preexposure levels may be used if found necessary. The intensity of the preexposure is very low, e.'g., about l/2,500 to 1/400 the exposure required to provide fully exposed areas, i.e., the exposure corresponding to the D of the positive image.

It should now be apparent that this invention provides a method for maintaining the photographic consistency of a total diffusion transfer system, notwithstanding normal variations in manufacture and ageing of the components. The herein disclosed use of preexposure to modify andadjust the sensitometry of a multicolor system has found to be a very effective method of modifying the color balanace of a multicolor diffusion transfer film. This method reduces the need for modification of the processing composition for use with manufacturing variants of the multicolor photosensitive element. The rebalancing method is one which permits maximum flexibility in the manufacturing and coating operations so that only a minimum of photosensitive material need be deemed unusable as out of specification" with respect to color balance. The rebalancing method is brought into operation at a relatively late stage of the film manufacturing operation, providing the ability to adjust after the photographic system has aged to equilibrium values.

Although this invention has been illustrated by the use of dye developers, it will be understood that it may advantageously be employed with other imaging systems wherein the image-forming components are initially diffusible or initially non-diffusible. The photosensitive element may be of the multilayer type, as in the illustrative disscussion,'or of the screen type such as described in US. Pat. No. 2,968,554.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A multicolor photosensitive element for use in forming diffusion transfer images comprising a support carrying a blue-sensitive silver halide emulsion, a

green-sensitive silver halide emulsion and a reds'ensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing material, and a cyan image dye-providing material, at least one of said silver halide emulsions containing a weak uniform latent image formed by uniform exposure of said photosensitive element, after coating of said silver halide emulsions, to light of a predetermined wavelength range, said preexposure being of an intensity and wavelength range adapted to bring the slopes of the D log E curves of the positive transfer images obtained from said silver halide emulsions following image-wise exposure into a more nearly parallel relationship with each other.

2; A multicolor photosensitive element as defined in claim 1 wherein at least two of said silver halide emulsions contain a weak uniform latent image, each of said uniform latent images being formed by uniform exposure of said photosensitive element to light of a predetermined wavelength range.

3. A multicolor photosensitive element as defined in claim 1 wherein uniform exposure is to a first wavelength range which exposes each of said silver halide emulsions as well as to a second wavelength range which provides an additional exposure of at least one of said silver halide emulsion.

4. A multicolor photosensitive element as defined in claim 1 wherein said green-sensitive silver halide emulsion and said red-sensitive silver halide emulsion each contain a weak uniform latent image.

5. A multicolor photosensitive element as defined in claim 1 wherein each said image dye-providing material is.a dye developer.

6. A photographic film unit adapted to be exposed and processed to produce a diffusion transfer image in color and comprising, in combination:

a laminate including two dimensionally stable layers and a plurality of layers intermediate said dimensionally stable layers, at least one of said dimensionally stable layers being transparent, said plurality of layers including an image-receiving layer and a blue-sensitive silver halide emulsion, a greensensitive silver halide emulsion and a red-sensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing material, and a cyan image dye-providing material, at least one of said silver halide emulsions containing a weak uniform latent image formed by uniform exposure of said photosensitive element, after coating of said silver halide emulsions, to light of a predetermined wavelength range, said preexposure being of an intensity and wavelength range adapted to bring the slopes of the D log E characteristic curves of the positive transfer images obtained from said silver halide emulsions following imagewise exposure into a more parallel relationship with each other, and

a rupturable container releasably retaining a fluid processing composition, said rupturable container being coupled to said laminate in position to discharge its liquid contents for spreading between a predetermined pair of said layers of said laminate to thereby cause delamination of said laminate between said predetermined layers thereof.

7. A photographic film unit as defined in claim 6 wherein each of said dimensionally stable layers comprise polyethylene terephthalate.

8. A photographic film unit as defined in claim 6 wherein said laminate includes a stratum of a high molecular weight polyethene glycol between the said surfaces of said predetermined layers at which delamination is effected by spreading of said processing composition.

9. A photographic film unit as defined in claim 6 wherein said processing composition includes titanium dioxide and is adapted, upon being distributed between said predetermined layers, of providing a lightreflecting layer capable of masking the developed silver halide emulsion layers.

10. A photographic film unit as defined in claim 6 wherein said image-receiving layer is supported on said transparent dimensionally stable layer and said silver halide emulsion layers are supported on said other dimensionally stable layers, said other dimensionally stable layers being opaque.

11. A photographic film unit as defined in claim 6 wherein atleast two of said silver halide emulsions contain a weak uniform latent image, each of said latent images being formed by uniform exposure of said photosensitive element to light of a predetermined wavelength range.

12. A photographic film unit as defined in claim 6 wherein uniform exposure is to a first wavelength range which exposes each of said silver halide emulsions as well as to a second wavelength range which provides an additional exposure of at least one of said silver halide emulsion.

13. A photographic film unit as defined in claim 6 wherein said green-sensitive silver halide emulsion and said red-sensitive silver halide emulsion each contain a weak latent image.

14. A photographic film unit as defined in claim 6 wherein each said image dye-providing material is a dye developer.

15. A photographic film unit as defined in claim 6 wherein said uniform latent image is of an intensity such that any reduction in said positive image reflection density resulting from said uniform exposure is no greater than about 0.1 to about 0.2.

16. The method of improving the sensitometry of a multicolor photosensitive element, said element comprising a blue-sensitive silver halide emulsion, a greensensitive silver halide emulsion and a red-sensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing material and a cyan image dye-providing material, said method comprising imparting a weak uniform latent image to at least one of said silver halide emulsions prior to photoexposing said silver halide emulsions imagewise, said weak uniform latent image being formed by a uniform low intensity exposure to light of a predetermined wavelength range.

17. The method as defined in claim 16 wherein each said image dye-providing material is a dye developer.

18. A method of manufacturing a multicolor photosensitive element for use in a multicolor diffusion transfer process, said method comprising the steps of (a) coating a multicolor photosensitive element comprising a support carrying a blue-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a redsensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing material, and a cyan image dye-providing material; (b) exposing a sample section of said multicolor photosensitive element to a color sensitometry target; (0) diffusion transfer processing said exposed multicolor photosensitive element and analyzing the resulting multicolor transfer image to determine the blue, green and red D log E characteristic curves of said transfer image as obtained from said blue-, green-, and red-sensitive silver halide emulsions thus processed and the deviation of each from a desired aim characteristic curve; and (d) uniformly exposing the remaining multicolor photosensitive element to light of a predetermined wavelength range and intensity to provide a weak uniform latent image in at least one of said silver halide emulsions, said weak uniform latent image being effective to modify at least one of said initial characteristic curves to more closely correspond with said desired characteristic curve.

19. The method as defined in claim 18 wherein said silver halide layers are temporarily laminated between polymeric support layers being-substantially impermeable to oxygen transmission, at least one of said support layers being transparent.

20. The method as defined in claim 18 wherein said silver halide layers are temporarily laminated between polyethylene terephthate support layers, at least one of said support layers being transparent.

21. The method as defined in claim 19 wherein said temporary lamination is effected prior to said uniform exposure.

22. The method as defined in claim 18 wherein said uniform exposure is applied after said photosensitive layer, the image-receiving system and the processing composition have completed their respective ageing process.

23. A photographic product which comprises a first polymeric support substantially impermeable to oxygen, a red-sensitive silver halide emulsion; a greensensitive silver halide emulsion; and a blue-sensitive silver halide emulsion; said silver halide emulsions having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer; an image-receiving layer for receiving image dyes transferred thereto as a function of exposure and development of said silver halide emulsion layers; a second polymeric support which is transparent and through which said image-receiving layer may be viewed; a rupturable container releasably holding a processing composition adapted, upon distribution between predetermined layers of said product to develop said silver halide emulsions and to effect the formation of a transfer image in dye in said image-receiving layer, said processing composition also being adapted to provide a permanent laminate including said developed silver halide emulsions and said image-receiving layer; and means providing a light-reflecting layer between said image-receiving layer and said silver halide emulsions effective to provide a white background for viewing said transfer image and for masking said developed silver halide emulsions; said polymeric supports being substantially impermeable to oxygen; said layers being bonded to each other between said polymeric supports to form a laminate which includes a predetermined pair of layers having a bond therebetween which is weaker than the bond between other layers whereby said processing composition may be distributed therebetween by delaminating said predetermined pair of layers; at least one of said silver halide emulsions containing a weak uniform latent image formed by substantially uniform exposure of at least one of said silver halide emulsions to a predetermined intensity and wavelength range of light.

24. Apparatus for assembling a diffusion transfer film unit comprising, in combination:

a. means for supplying a first element including photosensitive silver halide layers;

b. means for supplying a second element to be attached to said first element in superposed or superposable relationship with said photosensitive silver halide layers;

c. means for supplying a rupturable container for each film unit, said rupturable container releasably holding a processing composition;

d. means for advancing and securing said first and said second elements in superposed or superposable relationship with said rupturable container positioned to discharge its contents between predeterrnined layers carried between the supports of said elements when superposed; and

e. means for providing a uniform exposure to said photosensitive element at some stage of said assembly operation.

25. Apparatus as defined in claim 24 further including means for temporarily laminating said first and second elements together with said photosensitive layers between the outer layers forming said laminate, said photosensitive layers being exposable through one of said outer layers.

26. Apparatus as defined in claim 25 wherein said means for uniformly exposing said photosensitive element is positioned after said laminating means.

27. Apparatus as defined in claim 24 wherein said means for uniformly exposing said photosensitive element comprise a stroboscopic light source and means for positioning at least one light filter between said light source and said photosensitive element.

28. The method as defined in claim 21 wherein said laminate has completed its ageing process prior to said uniform exposure.

29. A multicolor photosensitive element for use in forming diffusion transfer images comprising a support carrying a blue-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a redsensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing mateiral, and a cyan image dye-providing material, at least one of said silver halide emulsions containing a weak uniform latent image formed by uniform exposure of said photosensitive element, after coating of said silver halide emulsions, to light of a predetermined wavelength range, said preexposure being of an intensity and wavelength range adapted to modify the D log E curves of the positive transfer images obtained from said silver halide emulsions following imagewise exposure to more closely correspond with predetermined D log E curves.

v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3 .819 .376 D'ated June 25 q 1974 Inventofls) Edwin H. Land It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 12, line 41, "unsing" should be -using-.

Column 12, line 51, "D log and E" should be --D log E--.

' Column 14, line 12 "disscussion" should be --discussion-.

Column 15, line 46, before "latent" (second occurrence) insert -uniform--.

Column 15', line 59, before "latent" insert --uniform.

Column 16, line 32 after "multicolor" insert -color--.

Column 16, line 53-, "terephthate" should be --terephtha1ate.

o Column 18, line 32, "mateiral" should be --material--.

Signed and sealed this 19th day of November 1974.

(SEAL) Attest:

' McCOY M. GIBSONJR. v C. MARSHALL DANN' Attesting Officer Commissioner of Patents F ORM PO-OSO (10-69) USCOMM-DC 0O376-P69 9 U. S. GOVIRNIIINT PRINTING OFFICE I." 0-36-334 

2. A multicolor photosensitive element as defined in claim 1 wherein at least two of said silver halide emulsions contain a weak uniform latent image, each of said uniform latent images being formed by uniform exposure of said photosensitive element to light of a predetermined wavelength range.
 3. A multicolor photosensitive element as defined in claim 1 wherein uniform exposure is to a first wavelength range which exposes each of said silver halide emulsions as well as to a second wavelength range which provides an additional exposure of at least one of said silver halide emulsion.
 4. A multicolor photosensitive element as defined in claim 1 wherein said green-sensitive silver halide emulsion and said red-sensitive silver halide emulsion each contain a weak uniform latent image.
 5. A multicolor photosensitive element as defined in claim 1 wherein each said image dye-providing material is a dye developer.
 6. A photographic film unit adapted to be exposed and processed to produce a diffusion transfer image in color and comprising, in combination: a laminate including two dimensionally stable layers and a plurality of layers intermediate said dimensionally stable layers, at least one of said dimensionally stable layers being transparent, said plurality of layers including an image-receiving layer and a blue-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a red-sensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing material, and a cyan image dye-providing material, at least one of said silver halide emulsions containing a weak uniform latent image formed by uniform exposure of said photosensitive element, after coating of said silver halide emulsions, to light of a predetermined wavelength range, said preexposure being of an intensity and wavelength range adapted to bring the slopes of the D log E characteristic curves of the positive transfer images obtained from said silver halide emulsions following imagewise exposure into a more parallel relationship with each other, and a rupturable container releasably retaining a fluid processing composition, said rupturable container being coupled to said laminate in position to discharge its liquid contents for spreading between a predetermined pair of said layers of said laminate to thereby cause delamination of said laminate between said predetermined layers thereof.
 7. A photographic film unit as defined in claim 6 wherein each of said dimensionally stable layers comprise polyethylene terephthalate.
 8. A photographic film unit as defined in claim 6 wherein said laminate includes a stratum of a high molecular weight polyethene glycol between the said surfaces of said predetermined layers at which Delamination is effected by spreading of said processing composition.
 9. A photographic film unit as defined in claim 6 wherein said processing composition includes titanium dioxide and is adapted, upon being distributed between said predetermined layers, of providing a light-reflecting layer capable of masking the developed silver halide emulsion layers.
 10. A photographic film unit as defined in claim 6 wherein said image-receiving layer is supported on said transparent dimensionally stable layer and said silver halide emulsion layers are supported on said other dimensionally stable layers, said other dimensionally stable layers being opaque.
 11. A photographic film unit as defined in claim 6 wherein at least two of said silver halide emulsions contain a weak uniform latent image, each of said latent images being formed by uniform exposure of said photosensitive element to light of a predetermined wavelength range.
 12. A photographic film unit as defined in claim 6 wherein uniform exposure is to a first wavelength range which exposes each of said silver halide emulsions as well as to a second wavelength range which provides an additional exposure of at least one of said silver halide emulsion.
 13. A photographic film unit as defined in claim 6 wherein said green-sensitive silver halide emulsion and said red-sensitive silver halide emulsion each contain a weak latent image.
 14. A photographic film unit as defined in claim 6 wherein each said image dye-providing material is a dye developer.
 15. A photographic film unit as defined in claim 6 wherein said uniform latent image is of an intensity such that any reduction in said positive image reflection density resulting from said uniform exposure is no greater than about 0.1 to about 0.2.
 16. The method of improving the sensitometry of a multicolor photosensitive element, said element comprising a blue-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a red-sensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing material and a cyan image dye-providing material, said method comprising imparting a weak uniform latent image to at least one of said silver halide emulsions prior to photoexposing said silver halide emulsions imagewise, said weak uniform latent image being formed by a uniform low intensity exposure to light of a predetermined wavelength range.
 17. The method as defined in claim 16 wherein each said image dye-providing material is a dye developer.
 18. A method of manufacturing a multicolor photosensitive element for use in a multicolor diffusion transfer process, said method comprising the steps of (a) coating a multicolor photosensitive element comprising a support carrying a blue-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a red-sensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing material, and a cyan image dye-providing material; (b) exposing a sample section of said multicolor photosensitive element to a color sensitometry target; (c) diffusion transfer processing said exposed multicolor photosensitive element and analyzing the resulting multicolor transfer image to determine the blue, green and red D log E characteristic curves of said transfer image as obtained from said blue-, green-, and red-sensitive silver halide emulsions thus processed and the deviation of each from a desired aim characteristic curve; and (d) uniformly exposing the remaining multicolor photosensitive element to light of a predetermined wavelength range and intensity to provide a weak uniform latent image in at least one of said silver halide emulsions, said weak uniform latent image being effective to modify at least one of said initial characteristic curves to more closely correspond with said dEsired characteristic curve.
 19. The method as defined in claim 18 wherein said silver halide layers are temporarily laminated between polymeric support layers being substantially impermeable to oxygen transmission, at least one of said support layers being transparent.
 20. The method as defined in claim 18 wherein said silver halide layers are temporarily laminated between polyethylene terephthate support layers, at least one of said support layers being transparent.
 21. The method as defined in claim 19 wherein said temporary lamination is effected prior to said uniform exposure.
 22. The method as defined in claim 18 wherein said uniform exposure is applied after said photosensitive layer, the image-receiving system and the processing composition have completed their respective ageing process.
 23. A photographic product which comprises a first polymeric support substantially impermeable to oxygen, a red-sensitive silver halide emulsion; a green-sensitive silver halide emulsion; and a blue-sensitive silver halide emulsion; said silver halide emulsions having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer; an image-receiving layer for receiving image dyes transferred thereto as a function of exposure and development of said silver halide emulsion layers; a second polymeric support which is transparent and through which said image-receiving layer may be viewed; a rupturable container releasably holding a processing composition adapted, upon distribution between predetermined layers of said product to develop said silver halide emulsions and to effect the formation of a transfer image in dye in said image-receiving layer, said processing composition also being adapted to provide a permanent laminate including said developed silver halide emulsions and said image-receiving layer; and means providing a light-reflecting layer between said image-receiving layer and said silver halide emulsions effective to provide a white background for viewing said transfer image and for masking said developed silver halide emulsions; said polymeric supports being substantially impermeable to oxygen; said layers being bonded to each other between said polymeric supports to form a laminate which includes a predetermined pair of layers having a bond therebetween which is weaker than the bond between other layers whereby said processing composition may be distributed therebetween by delaminating said predetermined pair of layers; at least one of said silver halide emulsions containing a weak uniform latent image formed by substantially uniform exposure of at least one of said silver halide emulsions to a predetermined intensity and wavelength range of light.
 24. Apparatus for assembling a diffusion transfer film unit comprising, in combination: a. means for supplying a first element including photosensitive silver halide layers; b. means for supplying a second element to be attached to said first element in superposed or superposable relationship with said photosensitive silver halide layers; c. means for supplying a rupturable container for each film unit, said rupturable container releasably holding a processing composition; d. means for advancing and securing said first and said second elements in superposed or superposable relationship with said rupturable container positioned to discharge its contents between predetermined layers carried between the supports of said elements when superposed; and e. means for providing a uniform exposure to said photosensitive element at some stage of said assembly operation.
 25. Apparatus as defined in claim 24 further including means for temporarily laminating said first and second elements together with said photosensitive layers between the outer layers forming said laminate, said photosensitive layers being exposable through one of said outer layers.
 26. Apparatus as defined in claim 25 wherein said means for uniformly exposing said photosensitive Element is positioned after said laminating means.
 27. Apparatus as defined in claim 24 wherein said means for uniformly exposing said photosensitive element comprise a stroboscopic light source and means for positioning at least one light filter between said light source and said photosensitive element.
 28. The method as defined in claim 21 wherein said laminate has completed its ageing process prior to said uniform exposure.
 29. A multicolor photosensitive element for use in forming diffusion transfer images comprising a support carrying a blue-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a red-sensitive silver halide emulsion, each of said silver halide emulsions having associated therewith, respectively, a yellow image dye-providing material, a magenta image dye-providing mateiral, and a cyan image dye-providing material, at least one of said silver halide emulsions containing a weak uniform latent image formed by uniform exposure of said photosensitive element, after coating of said silver halide emulsions, to light of a predetermined wavelength range, said preexposure being of an intensity and wavelength range adapted to modify the D log E curves of the positive transfer images obtained from said silver halide emulsions following imagewise exposure to more closely correspond with predetermined D log E curves. 